Spectral and Ritz 4DVAR preconditioning

[arango]

We added the spectral and Ritz precoditioning to the incremental strong constraint 4DVAR (IS4DVAR) algorithm which uses the approximated Hessian eigenvectors and Lanczos vectors during minimization of the cost function. This precoditioning is still under testing and we will let you when it is ready to use. Many thanks to Andy Moore for coding this algorithm.

I also updated the 4DVAR adjustment of surface forcing to account for the different options in ROMS for surface tracer flux. Many thanks to Gregoire Broquet for bringing this to my attention.